This invention relates to a method of and system for encoding a signature into a digital image.
Various images in traditional print or photographic media are commonly distributed to many users. Examples include the distribution of prints of paintings to the general public and photographs and film clips to and among the media. Owners may wish to audit usage of their images in print and electronic media, and so require a method to analyze print, film and digital images to determine if they were obtained directly from the owners or derived from their images. For example, the owner of an image may desire to limit access or use of the image. To monitor and enforce such a limitation, it would be beneficial to have a method of verifying that a subject image is copied or derived from the owner""s image. The method of proof should be accurate and incapable of being circumvented. Further, the method should be able to detect unauthorized copies that have been resized, rotated, cropped, or otherwise altered slightly.
In the computer field, digital signatures have been applied to non-image digital data in order to identify the origin of the data. For various reasons these prior art digital signatures have not been applied to digital image data. One reason is that these prior art digital signatures are lost if the data to which they are applied are modified. Digital images are often modified each time they are printed, scanned, copied, or photographed due to unintentional xe2x80x9cnoisexe2x80x9d created by the mechanical reproduction equipment used. Further, it is often desired to resize, rotate, crop or otherwise intentionally modify the image. Accordingly, the existing digital signatures are unacceptable for use with digital images.
The invention includes a method and system for embedding image signatures within visual images, applicable in the preferred embodiments described herein to digital representations as well as other media such as print or film. The signatures identify the source or ownership of images and distinguish between different copies of a single image.
In a preferred embodiment described herein, a plurality of signature points are selected that are positioned within an original image having pixels with pixel values. The pixel values of the signature points are adjusted by an amount detectable by a digital scanner. The adjusted signature points form a digital signature that is stored for future identification of subject images derived from the image.
The foregoing and other features of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.